Tracking a moving object in real time is quite easy these days thanks to available GPS chips on location enabled UEs such as mobile stations. Similarly, finding how long it would take for a moving object to reach a certain place at any given point is also possible if the terrestrial route data between the source and destination is available. However, accurately finding which all places of interest is reachable within a given time period is somewhat computationally intensive task. The complexity of this problem grows dramatically as the number of objects to be tracked and their area of movement grows. Accurately tracking millions of user equipments with limited resources in real time against millions of points of interest is still a big technical challenge.
Geo-fences technology solves this problem to a great extent (see for instance http://en.wikipedia.org/wiki/Geofence). It allows a location service to define a virtual fence around a target region or POI, and to raise an alert whenever a tracked object of interest, e.g. a MS, crosses it. The biggest limitation of this technology is that it uses the aerial distance between the tracked object and the fenced region instead of the distances along the actual terrestrial routes. In local context, usually the aerial distance between two geographic locations is not an accurate indicator of the travel time between them. There are several reasons for such limitations:
freeways are one way and have limited exits and entry points,
some streets can be one way,
some areas are bounded and have only a few entry/exit points,
some areas have rail road, canals etc running through them.
For example, in order to figure out which POIs are within walking distance of a user, it is not sufficient to know just the user's location. It is important to know the actual route data between the POI and the user. In this scenario the current geo-fences implementations will end up providing inaccurate results in most of the cases.
Today there is still a need for an improved geo-fence that addresses the limitations of the known circular geo-fences. There is a further need for a computationally simple solution that can be used with location services.